PROJECT SUMMARY/ABSTRACT The overarching goal of this research is to reveal the brain mechanisms by which visual attention, visual short- term memory (STM) and retrieval from visual long-term memory (LTM) integrate their functioning to support cognition and perception. Performance of healthy humans in visual tasks exceeds the performance of supercomputers, yet the capacity of the human visual system is profoundly limited; people can only attend to or hold in visual STM about four objects at one time. Retrieval from long-term memory into visual working memory (VWM) contributes greatly to visual performance in familiar contexts. However, diseases, including Alzheimer's and schizophrenia, traumatic brain injuries, stroke, and normal aging all can lead to reductions in the capacity of visual attention and STM and result in severe impairments in the performance of vision-related cognitive and perceptual tasks. In order to help guide therapeutic interventions, it is critical to have a detailed understanding of the neural substrates and mechanisms of visual attention, STM and LTM retrieval. A series of human functional magnetic resonance imaging (fMRI) and behavioral studies is proposed to identify the shared and dissociated neural substrates of visual attention, visual STM and retrieval from visual LTM. Research has shown that portions of the frontal and parietal lobes work together as a network to support each of these tasks, but currently the precise identity and functional role of these brain areas in the different tasks is not well understood. Functional localizer fMRI methods and within-subject analysis will be performed in order to obtain precise localization of these brain regions. STM load and several attentional factors will be manipulated in order to identify the functional contributions of different brain regions to capacity limits under different forms of task demands. Event-related analysis will be performed in order to identify network components of visual LTM retrieval and their relationship to components of the visual STM, attentional & default mode networks. Experiments employing functional connectivity fMRI methods will focus on network interactions that may play a role in the symptoms of Hemispatial Neglect and in the post-stroke mechanisms that accompany restoration of spatial processing. This knowledge can guide the development of assays that can refine diagnosis and treatment of psychiatric illnesses and may help maintain cognitive function in persons who experience disease- related or age-related decline. As the specific contributions of different brain regions are characterized, research can focus on identifying particular network subcomponents that may be differentially impaired in different clinical populations.